1. Field of the Invention
This invention relates to a glass antenna system, and more particularly to an antenna system which uses an electrically powered window heater as an antenna element in the system.
2. Technical Considerations
It is well known in the art to provide glass windows in a motor vehicle that incorporate an antenna. In particular, an antenna pattern may be formed from electrically conductive ceramic paints applied and bonded to a surface of the glass window using techniques well known in the art. The window may also include a heater, typically in the form of a heating grid, to defog and/or de-ice the window surface. These grids generally include a pair of opposing electroconductive bus bars and a plurality of electroconductive heating lines which extend between the bus bars along the glass surface. If desired, the heating grid may be coupled to the antenna system to receive radio signals, for example as disclosed in U.S. Pat. Nos. 4,736,206 to Sakurai, et al. and 5,119,106 to Murakami. Coils are typically incorporated into an antenna system which uses the heater grid as part of the antenna to prevent the signal generated in the grid from being lost through a grounded connection. More specifically, coils are generally located between the antenna and the grounded connection to the antenna. For example, U.S. Pat. No. 5,581,264 to Tabata, et al. discloses the use of a choke coil to insulate the defogger system from ground in the broadcast frequency bands and high frequency wave coils to compensate for deteriorated characteristics of the choke coil in the high frequency wave range.
It would be advantageous to integrate more of the antenna system onto the glass so as to reduce costs, simplify the antenna design, and to allow designers to configure other components of the antenna system to be more compact.